Wiper arm with integral nut

ABSTRACT

The invention is a wiper arm ( 20 ) for securement to a drive shaft ( 10,12 ). The wiper arm ( 20 ) has a securing part ( 18 ), which on one end has a bearing point ( 16 ) by way of which the wiper arm can be connected, in a manner fixed against relative rotation, to the drive shaft ( 10, 12 ) via a nut ( 14 ). The nut can be screwed onto the drive shaft ( 10,12 ). The nut is formed by a component integrally cast onto the securing part ( 18 ) and is connected to the securing part ( 18 ) via a binding ( 26 ) that can be released upon installation of the wiper arm ( 20 ).

BACKGROUND OF THE INVENTION

The invention is based on an apparatus for securing a wiper arm to adrive shaft.

Wiper systems with a plurality of windshield wipers for motor vehiclesare secured with their wiper bearings to the body of the motor vehicledirectly or indirectly via a mounting plate. The mounting plate carriesa wiper drive with a wiper motor, whose motor shaft, via a rod linkage,drives cranks that are solidly connected to one end of a drive shaft foreach windshield wiper. It is also possible for only the drive shaft ofone windshield wiper to be driven by the wiper motor, while anotherwindshield wiper is connected to the first windshield wiper via afour-bar lever mechanism and has a bearing shaft. The drive shaft orbearing shaft is supported in a wiper bearing. The remarks belowpertaining to a drive shaft apply equally to a bearing shaft, which willno longer be expressly named.

At least one radial bearing is provided in the bearing housing, and oneaxial bearing is provided between the bearing housing and a part solidlyconnected to the drive shaft. The drive shaft protrudes out of thevehicle body and moves a wiper arm, secured on its free end, with awiper blade over a windshield. The wiper arm as a rule has a securingpart that is connected to the drive shaft in a manner fixed againstrelative rotation and is pivotably connected to a hinge part to which awiper rod is rigidly joined. It is also possible for the wiper arm notto be connected directly to the drive shaft but instead to be driven viaa lever mechanism with a drive lever connected to the drive shaft in amanner fixed against relative rotation. The following remarks pertainingto connecting the securing part to the drive shaft apply equally to adrive lever, which will no longer be expressly named.

In known windshield wipers, on one end the securing part has a bearingpoint with a female cone, with which in a first mounting step thesecuring part, upon mounting of the wiper arm, is placed on a suitablyshaped male cone of the drive shaft. Next, in a second mounting step, anut is screwed onto the drive shaft, and by way of this nut the securingpart is pressed with the female cone onto the male cone of the driveshaft. In order to achieve a positive engagement in addition to anonpositive engagement, it is known for knurled teeth or knurled cuttingedges to be integrally formed onto the cone of the drive shaft.Depending on the diameter of the drive shaft, from 29 to 44 knurledcutting edges are provided over the circumference; they are orientedlongitudinally of the drive shaft and have a triangular cross-sectionalarea with an angle of 90°. The height and cross-sectional area of theknurled cutting edges increase as the diameter of the cone increases, sothat the entire jacket face of the cone is covered with knurled cuttingedges.

SUMMARY OF THE INVENTION

The invention is based on an apparatus for securing a wiper arm to adrive shaft. The wiper arm has a securing part, which on one end has abearing point by way of which the securing part can be connected, in amanner fixed against relative rotation, to the drive shaft via a nutthat can be screwed onto the drive shaft.

It is proposed that the nut is formed by a component integrally castonto the securing part and is connected to the securing part via abinding that can be undone when the wiper arm is installed. Thisdispenses with one additional component, and the bearing outlay,logistical effort and mounting effort can be reduced and costs can besaved. If the wiper arm is shipped to the customer in the preassembledstate, the nut is connected in captive fashion to the securing part.This makes an additional premounting of the nut on the securing partunnecessary. The nut can be secured by the binding to various points ofthe securing part, but preferably the nut is disposed above the bearingpoint, in a mounting position; preferably, the binding is integrallyformed on between the face end of the nut pointing toward the securingpart and the securing part. The mounting can be done especially quicklyand economically and in particular can easily be automated. In themounting position, the nut can be grasped and screwed directly onto adrive shaft. The binding is advantageously formed by a thin-walledcylinder, which in terms of production technology is simple to form orcast integrally.

In one feature of the invention, it is proposed that the securing partis supported with the bearing point via a female cone on a male cone ofthe drive shaft, and the drive shaft has teeth, integrally formed ontothe male cone, by way of which teeth both a nonpositive and a positiveengagement can be made between the drive shaft and the securing part,the height of the teeth remaining constant over the jacket face of thecone. In the mounting process, the teeth deform the material of thesecuring part uniformly. The securing part can be made to rest on theentire conical jacket face of the drive shaft with an only slighttightening moment of a securing nut or with an only slight axial force.Inexpensive materials with low wall thicknesses can be employed.Furthermore, because of the low tightening moment required, the securingnut can especially advantageously be jointly cast onto the securing partin a single method step, comprising an inexpensive and lightweightmaterial, such as plastic, zinc, aluminum, magnesium, and so forth.

An only partial contact of the securing part on the tips of the teeth,especially in the lower region of the cone, can be avoided, and thenonpositive and positive engagement between the drive shaft and thesecuring part can be improved. Furthermore, inlay parts, especially inthe case of plastic securing parts, can be avoided.

The teeth can be integrally formed on using various methods that appearsuitable to one skilled in the art, such as non-metal-cutting creativeforming or reshaping, such as rolling with a knurling tool, extrusion,deep drawing in the case of components made from sheet metal, or bymetal-cutting methods, such as milling, broaching, and so forth. Theteeth can also have various shapes, such as pyramid-shaped, conical, andso forth. In one feature of the invention, it is propose that the teethare formed by cutting edges oriented essentially in the longitudinaldirection, which in the longitudinal direction have a constant heightand preferably have a constant cross-sectional area. Cutting edgesoriented in the longitudinal direction can be produced especiallyeconomically and bring about a good positive engagement.

It is also proposed that the spacing in the circumferential directionbetween each two teeth at the same axial height on the drive shaft isadapted to the tensile strength of the materials used for the driveshaft and for the securing part, and with decreasing tensile strength ofthe material for the securing part relative to the tensile strength ofthe material for the drive shaft, the spacing between the teethincreases.

The shear strength of the teeth on the drive shaft and of the materialcomprising the securing part that is located between the teeth can befitted to one another, and overall, the highest possible shear strengthand the highest possible transmissible torque can be achieved at only aslight tightening moment of the securing nut. If the spacing in thecircumferential direction is relatively great, then fewer teeth can bemounted on the cone for the same diameter of the drive shaft. If theteeth are integrally formed onto a male cone of a steel drive shaft thathas a rated diameter of 8 mm below the cone and according to DIN has asurface hardness of at least 135 HBS to 200 HBS, then advantageouslyfrom 30 to 40 cutting edges for a steel securing part, 20 to 30 cuttingedges for a zinc or aluminum securing part, 15 to 25 cutting edges for amagnesium securing part, and 5 to 15 cutting edges for a plasticsecuring part, are advantageously integrally formed onto the drive shaftover the circumference of the conical jacket face. In drive shafts witha lesser or greater rated diameter, correspondingly fewer or morecutting edges are disposed over the circumference.

It is furthermore possible by means of the shape, width and especiallyheight of the teeth, to fit the allowable maximum loads in thecircumferential direction of the teeth and of-the material of thesecuring part located between the teeth to one another, and to achievean overall maximum allowable transmissible torque. Advantageously, theheight of the teeth increases as the tensile strength of the materialfor the securing part decreases relative to the tensile strength of thematerial for the drive shaft.

BRIEF DESCRIPTION OF THE DRAWING

Further advantages will become apparent from the ensuing drawingdescription. In the drawing, exemplary embodiments of the invention areshown. The drawing, description and claims include numerouscharacteristics in combination. One skilled in the art will expedientlyconsider the characteristics individually as well and put them togetherto make useful further combinations.

Shown are:

FIG. 1, a detail of a wiper system having a wiper arm, in section;

FIG. 2, a securing part seen from above, before an initial mounting;

FIG. 3, a section taken along the line III—III of FIG. 2;

FIG. 4, a section taken along the line IV—IV of FIG. 1 without thesecuring part;

FIG. 5, an enlarged view of a drive shaft from above; and

FIG. 6, a variant of FIG. 4 for a securing part made of a material oflow tensile strength.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows a detail of a wiper system 36 for a motor vehicle, whosewiper bearings are secured to the body 40 of the motor vehicle via amounting plate 38. The mounting plate 38 carries a wiper drive with awiper motor 42, whose motor shaft 44, via a crank 46 and a rod linkagenot further shown, drives cranks 48 that are each solidly connected toone end of a drive shaft 10 for a windshield wiper. The drive shaft 10is supported (FIG. 4) in a bearing housing 56 of the wiper bearingradially via bearing bushes 50, 52 and in a first axial direction via acrank arm 54 and in a second axial direction via a clamping ring 58 anda runner ring 60. The drive shaft 10 protrudes out of the body 40 andmoves a wiper arm 20, secured by its free end, with a wiper blade notshown in further detail over a windshield (FIG. 1). The wiper arm 20 hasa securing part 18, which is pivotably connected via a toggle joint 62to a hinge part 64, which is rigidly adjoined by a wiper rod 66. Thewiper blade is suspended from a bracketlike end 68 of the wiper rod 66.The securing part on one end has a bearing point 16, by way of which thesecuring part 18 can be connected in a manner fixed against relativerotation to the drive shaft 10, via a nut 14 that can be screwed ontothe drive shaft 10.

According to the invention, the nut 14 is formed by a componentintegrally cast onto the securing part 18 and is connected to thesecuring part 18 via a binding 26 that can be undone upon mounting ofthe wiper arm 20 (FIGS. 2 and 3). The nut 14 is disposed above thebearing point 16 in a mounting position, and the binding 26 is formedintegrally in the form of a thin-walled cylinder between the face end ofthe nut 14, pointing toward the securing part 18, and the securing part18 itself. The binding 26 breaks as soon as the nut, on being screwedonto the drive shaft 10, is loaded with a torque. The securing part 18and the nut 14 are made of aluminum in a single method step,specifically a die-casting process. It is also possible to make thesecuring part and the nut of plastic, zinc, magnesium, and so forth.

The drive shaft 10 comprises a harder material than the securing part18, and on a male cone 70 it has teeth or knurled cutting edges 22,oriented longitudinally of the shaft, which in the mounting of thesecuring part 18 on the drive shaft 10 are pressed into a jacket face ofa female cone 72 of the securing part 18 and establish not only anonpositive but also a positive engagement between the drive shaft 10and the securing part 18 (FIGS. 1, 4 and 5). According to the invention,the knurled cutting edges 22 have a constant height 32 in thelongitudinal direction; that is, they are the same height as one anotherfrom the base of the tooth to the tip of the tooth, and they preferablyhave a constant cross-sectional area. This creates smooth conical jacketfaces 74 between the knurled cutting edges 22.

Upon mounting, the material of the securing part 18 is deformeduniformly over the length of the knurled cutting edges 22. The securingpart 18 can be brought to rest with a low tightening moment using thenut 14 or with a slight axial force on the entire conical jacket face ofthe drive shaft 10. The securing part 18 is prevented from resting onlypartly on the tips of the knurled cutting edges 22, especially in thelower region of the male cone 70, and a good nonpositive and positiveengagement is achieved between the drive shaft 10 and the securing part18.

In FIG. 6, a drive shaft 12 with knurled cutting edges 24 is shown for asecuring part which is made from a material of lesser tensile strengththan the securing part 18, specifically for a securing part ofmagnesium. The spacing 30 between the knurled cutting edges 24 isgreater than the spacing 28 between the knurled cutting edges 22 in theexemplary embodiment of FIG. 5. For the same diameter of the driveshafts 10 and 12, fewer knurled cutting edges 24 are formed integrallyonto the drive shaft over its circumference. The shear strength of theknurled cutting edges 24 on the drive shaft 12 and of the material ofthe securing part existing between the knurled cutting edges 24 arefitted to one another, so that overall the maximum possible shearstrength and the maximum allowable transmissible torque are achieved. Tofit the allowable maximum stress on the knurled cutting edges 24 and onthe material between the knurled cutting edges 24 of the securing partto one another, the knurled cutting edges 24 furthermore have a greaterheight 34 than the knurled cutting edges 22. As in the exemplaryembodiment of FIGS. 1-5, however, the knurled cutting edges 24 have aconstant height 34 and a constant cross-sectional area in thelongitudinal direction.

What is claimed is:
 1. A wiper arm (20) for securing a drive shaft (10,12), in which the wiper arm (20) has a securing part (18), which on oneend has a bearing point (16) by way of which the securing part (18) canbe connected, in a manner fixed against relative rotation, to the driveshaft (10, 12) via a nut (14) that can be screwed onto the drive shaft(10, 12), characterized in that the nut (14) is formed by a componentintegrally cast as one piece with the securing part (18) and isconnected to the securing part (18) via a binding (26) that can beundone when the wiper arm (20) is installed.
 2. The wiper arm of claim1, characterized in that the nut (14) is disposed above the bearingpoint (16), in a mounting position.
 3. The wiper arm of claim 2,characterized in that the binding (26) is integrally formed on andbetween a face end of the nut (14) pointing toward the securing part(18) and the securing part (18).
 4. The wiper arm of claim 3,characterized in that the binding (26) is formed by a thin-walledcylinder.
 5. The wiper arm of claim 1, characterized in that thesecuring part (18) is supported with the bearing point (16) via a femalecone (72) on a male cone (70) of the drive shaft (10, 12), and the driveshaft (10, 12) has teeth (22, 24), integrally formed onto the male cone(70), by way of which teeth both a nonpositive and a positive engagementcan be made between the drive shaft (10, 12) and the securing part (18),a height (32, 34) of the teeth (22, 24) remaining constant over a jacketface of the cone.
 6. The wiper arm of claim 5, characterized in that theteeth (22, 24) are formed by cutting edges oriented essentially in alongitudinal direction.
 7. The wiper arm of claim 5 characterized inthat a spacing (28, 30) in a circumferential direction between each twoteeth (22, 24) at a same axial height on the drive shaft (10, 12) isadapted to the tensile strength of the materials used for the driveshaft (10, 12) and for the securing part (18) such that as the tensilestrength of the material for the securing part (18) decreases relativeto the tensile strength of the material for the drive shaft (10, 12),the spacing (28, 30) between the teeth (22, 24) increases.
 8. The wiperarm of claim 5, characterized in that the height (32, 34) of the teeth(22, 24) is adapted to the tensile strength of the materials used forthe drive shaft (10, 12) and for the securing part (18) such that as thetensile strength of the material for the securing part (18) decreasesrelative to the tensile strength of the material for the drive shaft(10, 12), the height (32, 34) of the teeth (22, 24) increases.